cj9694

Has anyone ever installed a trans cooler for the Miata 5 speed? I have heard the main failure mode for the trans is due to the trans heating up, case deforming some (twisting) and then the gears misalign and eat themselves. I was thinking about installing a pump and cooler at the the fill and drain holes to mitigate that (install a filter while I'm at it). The reason I ask is because I'm looking to do an FE3 swap and the easiest route to that swap is putting a b2000 bellhousing on a Miata 5 speed but the trans is known to fall apart above 250hp. I've been talking to M2CupCar about his swap and he's running +300hp on the Miata trans till it blows up and then bolts in a new one. I know a few racers that have ecotecs with the solstice trans that has similar heat issues and run trans cooler and hasn't nuked a trans since. Just wondering what everyone thinks about a cooler, if anyone has run one, and if anyone has a link to their install. Thanks!

Savington

iTrader: (31)

The main failure mode is stripping gears due to excess torque capacity. Could be case flex, but heat has nothing to do with it. They break at 200whp with cold fluid if you beat on them hard enough (hard shift + pucked clutch). A cooler will do nothing IMO.

cj9694

So then would Cryo treatment or REM finishing the gears make the trans stronger?

cj9694

And I'm talking endurance road racing not drag racing. And a sprung non puck clutch

codrus

Relatively few people have looked into ways to extend the life of the 5-speed, because generally when you blow one of those up on a Miata you just put in a 6-speed instead.

Efforts to extend the life of a 6-speed have generally not been very fruitful either.

--Ian

DeerHunter

Sav is correct in that the OEM gears are the weak point in the 5-speed. Your supposition about the failure point, at least in my opinion, only holds water when you have replaced them with stronger gears. My street/autocross car makes north of 300 lb-ft and lived happily with a complete Quaife gearset in the stock transmission housing. When our local track opened up and I started doing HPDEs, my tranny lunched itself within a few months. Failure mode was a single stripped gear.

I replaced the entire box with another Quaife setup and repeated myself within a few months (different gear, but same type of failure). I considered adding a cooler when I had that box rebuilt but ultimately just retired that car from track duty. I now run an MSM with FM II upgrade and have had no more gearbox woes (although the 6-speed doesn't shift as nicely as the 5-speed).

So, to your original point, the Quaife gears are strong enough for the torque I make. When tracked, heat build-up causes the case to flex, the gears no longer align nicely and eventually a tooth breaks. Again, just my opinion, although the thinking is borne out by the fact that the long transmission housing bolts tend to snap under the aforementioned conditions.

Cheapest solution, as suggested by Codrus, is to change to a 6-speed (although that's only a viable option if you make no more than about 250 lb-ft). Bulletproof option is the BMW tranny kit that's been developed by K-Miata.

Savington

iTrader: (31)

If you are going to make enough power to warrant the pain and suffering of the FE3 swap over just keeping a BP in the car, you need to look at other options beyond the 5-speed. It's not going to survive your application.

cj9694

Yeah, I have been. Trying to figure out all the components to make a R trans work, but the damn Kia 8 bolt crank makes it a challenge for getting a flywheel that will mesh with a starter on a Bongo or b2600 bellhousing. Otherwise I would just go that route.